Combustion chamber and diffusion nozzle arrangement for reducing over-all length of jet engines



Aug. 14, 1951 o, N. WALKER EI'AL 2,564,218

COMBUSTION CHAMBER AND DIFFUSION NOZZLE ARRANGEMENT FOR REDUCING OVERALLLENGTH OF JET ENGINES Filed Feb. 25, 1948 2 Sheets-Sheet 1 Aug. 14, 1951D. N. WALKER ETAL COMBUSTION CHAMBER AND DIFFUSION NOZZLE ARRANGEMENTFOR REDUCING OVERALL LENGTH OF JET ENGINES 2 Sheets-Sheet 2 Filed Feb.25, 1948 a u m mAftorney Patented Aug. 14, 1951 COMBUSTION CHAMBER ANDDIFFUSION NOZZLE ARRANGEMENT FOR REDUCING OVER-ALL LENGTH OF JET ENGINESDaniel Norman Walker, Coventry, Peter Frederick Ashwood, Old Coulsdon,

and Henry Cowan, Lutterworth, England, assignors to Power Jets (Researchand Development) Limitcd, London, England, a British company ApplicationFebruary 25, 1948, Serial No. 10,866 In Great Britain March 4, 1947Claims.

This invention relates to combustion apparatus for gaseous or liquidfuels and has for its object to provide a combustion apparatus suitablefor use in circumstances in which combustion has to be supported by afast moving ducted gas flow of flame-extinguishing velocity. Whilst, aswill be seen after consideration of its details, the invention haspossible applications in a wider field, it is primarily concerned and isat present conceived to have its maximum utility in connection withcombustion apparatus in which special problems arise due to thenecessity for supporting continuous combustion by means of a fast movinggaseous cin'rent involving a large mass flow, as

for example, in gas turbines or other jet propulsion power lmits and ingas turbines for other purposes. The description "fast moving as appliedto a combustion-supporting gas flow is used herein to indicate that themean speed of the gas in its general direction of flow past a combustionzone, calculated from the ratio air volume passing in unit time/crosssectional area of flow path, is substantiallv higher than the speed offlame propagation in the fuel/gas mixture concerned. For hydrocarbonfuels burning in air the speed of flame propagation is considered asbeing of the order of 1 foot per second at atmospheric tem-.- perature;the invention, on the other hand, is especially applicable to combustionapparatus for gas turbines or/and jet propulsion power units in whichthe speed of the air current in its general direction of flow past acombustion zone, calculated on the basis indicated, might be of an orderas low at 10 or as high as 300 feet per second or even more depending onthe design.

In combustion systems employing velocities of the order indicated, thegas flow must be 'difl'used before combustion can be effectivelymaintained. It has accordingly been the practice to employ a difiusersection of substantial length in series with the inlet to the apparatusand the combustion zone, which has necessarily involved undue length andweight of the apparatus. This difliculty is a serious one in powerplants, especially those for aircraft, of the combustion gas turbinetype in which a compressor supplies air by way of a combustion system toa turbine, in which case it is usual to efiect further diflfusion of theair emerging from the compressor before allowing it to enter thecombustion zone. Since in such a z case the combustion apparatus isusually arranged annularly about the common axis of the compressor andturbine, the inc ease of weight primarily to these that its applicationis contemplated, it may be applied in other cases where comparableproblems arise, in order to effect reduction of length of a combustionsystem even where there is no compressor. In achieving this object theinvention also seeks to enable stable combustion to be supported notonly by a fast moving gas flow but also with high air/fuel ratios andwith high rates of fuel injection and low pressure loss, all of whichare requirements further arising in connection with gas turbines and jetpropulsion units.

It will be assumed for the purpose of further consideration that acombustion apparatus according to the invention basically requires aduct suitable for carrying the air or other gas flow in which combustionis to be supported, and a combustion chamber within that duct whichdefines a zone of at least initial combustion.

With the foregoing in mind the invention provides for the combustionzone to be in overlapping relationship in the general direction of thegas flow with a diffusion system embodied in the ducting through whichpasses at least part of the combustion-supporting gas flow, the diffusersystem including diffuser nozzle means, structurally distinct from boththe combustion chamber and its enclosing duct, which is arranged toreceive gas from the supply and to effect under the conditions ofoperation controlled diffusion thereof before delivering it into acontinuation of the ducting downstream of the upstream limit of thecombustion zone. 1

A particular case to which the invention may be applied with advantageis that of a gas turbine power unit in which the motive fluid of theturbine is derived from a compressor (and more particularly a.centrifugal compressor) having a large number of outlets discharginginto a combustion system embodying a smaller number of combustionchambers than there are outlets, circumferentially arranged downstreamfrom the compressor outlets. According to a feature of the invention insuch a case the combustion chambers are enclosed in a common annular aircasing and constitute the principal, or only, outlet therefrom, and thecompressor outlets are united in pairs by diffuser nozzles eachembodying two diffuser passages merging together in V form to afford asingle outlet, or adjacent outlets separated by a splitter, and arrangedso that each pair of diffuser passages receives the output from a pairof adjacent compressor outlets, these diffuser nozzles extendingdownstream into the spaces between adjacent combustion chambers. In sucha case the upstream ends of the combustion chambers may be brought closeup to the rear face of the compressor, so that virtually no additionallength is required for diffusion of the compressor output after leavingthe compressor proper.

The foregoing features of the invention may with advantage be adapted tothe requirements of the invention by constructing the combustion chamberat its upstream end to direct a part only of a gas flow in the duct atone or more points into a radially inner part of a fuel jet or spraydirected upstream into the upstream limiting region of the combustionchamber.

An example of application of the invention is illustrated in theaccompanying drawings, in which Figure 1 is-a side elevation of acombustion gas turbine embodying a combustion apparatus in accordancewith the invention, the combustion section being in section on line 1-1of Figure 2 and the compressor and turbine sections being indicated inoutline only;

Figures 2 and 3 are half sections on lines 11-11 and Ill-IIIrespectively of Figure 1 looking in the directions of the arrows;

Figure 4 is a fragmentary view corresponding to the top left hand comerof the combustion apparatus as it appears in Figure 1 but embodying a.modified fuel injection arrangement.

Figures 5 (i) and (ii) show in elevation and sectional plan,respectively, a detail of Figure 1;

Figure 6 shows various sections of the detail shown in Figures5 (i) and(ii).

In the example illustrated, the invention is embodied in a gas turbinejet propulsion power unit comprising a multistage centrifugal compressorl discharging into a combustion section generally indicated as 2 whichsupplies the motive fluid of a turbine section 3 exhausting by way of apropulsive jet duct 4, the compressor, combustion section, and turbinebeing all coaxial and symmetrical with respect to a shaft 5 by which theturbine drives the compressor. The shaft 5 has an intermediate bearing 6housed in the downstream casing wall of the compressor, a forwardbearing 1 housed in a spider or annulus 8 attached at a radially outerregion (for the sake of rigidity) by means of studs 9 to the upstreamcasing wall of the compressor, and a rear bearing 10 housed in atransverse bearer member ll of girder-like structure whose outer endsare swept forwardly for attachment to a stifily constructed skirt l2extending radially outwardly from the turbine nozzle structure. Thepropulsive jet duct 4 at its upstream end forms a complete annulusreceiving the turbine exhaust, but is bifurcated to pass on either sideof the bearer member I I to twin jet orifices.

The combustion apparatus at 2 comprises an annular air duct defined byan air casing having an outer skin l3 and a tubular inner wall I4enclosing the shaft 5 and rigidly secured at its ends signed as a majorstress-carrying element tov form a backbone unifying the compressor andturbine units. The annulus thus formed accommodates a plurality (in thiscase six) of tubular combustion chambers l5 each of which is supportedat its upstream end by the. fuel supply connections iii of a fuelinjection nozzle I1, and at its downstream end is seated with freedomfor longitudinal expansion in a sleeve l8 bounding a circular aperturein an annular diaphragm wall IS. The sleeve l8 of each said aperturealso forms, externally, a seating for the upstream end of an outletchute 20 which merges in the downstream direction into the form of asegment of an annulus seating in the turbine nozzle structure, theoutlets of the chutes 20 collectively forming a virtually completeannulus corresponding to that of the turbine nozzle.

The compressor discharges at a plurality of outlets 2|, there beingtwice as many outlets as there are combustion chambers I5, and theseoutlets 2| are united in pairs by diffuser nozzles each embodying twodiffuser ducts 22A, 22B merging together in V form to afford a singleoutlet, or a virtually single outlet subdivided by splitters if requiredfor aerodynamic reasons. Each diffuser nozzle 22A-22B is made as a unitseparate from the remainder of the structure and bolted to the rear wallof the compressor so as to extend longitudinally between adjacentcombustion chambers l5 and discharge ata downstream zone of the aircasing.

The paired ducts 22A-22B, as shown in elevation and sectional plan inFigures 5 (i) and 5 (ii) and Figure 6, are made of suitable crosssection to effect the required gradual diffusion (the cross sections a,b, c, d and e (Figure 6) at the equidistant stations A, B, C, D and E ofFigures 5 (i) and (ii) changing smoothly from rectangular to circular)and the air casing is thus filled with air under pressure, which isallowed to enter the combustion chambers I 5 through axially spaced rowsof ports 23 suitably located therein by which the inlet flow is suitablyproportioned as between different zones corresponding respectively toprimary and secondary combustion and mixing stages.

The diaphragm I9 is apertured at 24 and has an annular clearance at 25to allow the entry of cooling air to the space enclosing the outletchutes 20, which in turn may, if desired, provide for a further stage ofentry of air into the hot working fluid.

In the example illustrated in Figure l the invention is arranged forinjection of fuel in an upstream direction (considered in relation tothe general direction of flow) behind a baille 26 disposed upstream ofthe fuel nozzle l1 and screening it from the air current and constructedto direct a part only of the main air supply at one or more points intoa radially inner region of the fuel jet. This baffle 26 which may, forexample, as shown, be in the form of a-cone having its apex directedtowards the fuel nozzle I1, and is ported at 21 to allow the controlledentry of pilot air to the inner region of the fuel jet, also forms theupstream end of the flame tube l5 by which the main body of air isconstrained to flow at a radially outer region with respect to the fueljet and is separated from the flame in the downstream direction. Such anarrangement allows the maximum advantage to be taken of the possibility,offered by the use of the diifusion nozzles 22A22B, of bringing theupstream end of each combustion chamber close up to the rear wall of thecompressor; the use of the nozzles fill-22B for diifusion, however, alsopermits the more conventional form of downstream fuel injectionillustrated in Figure 4 to be used with very little increase in theaxial length of the combustion system.

It will be appreciated that in either case combustion is enabled to takeplace, in eifect, within what would otherwise be exclusively a diffusionzone, thus permitting an economical overall length of the unit with aconsequent economy of space and weight.

We claim:

1. A combustion apparatus adapted to support combustion by means of afast moving gas flow comprising means for supplyingthe gas flow, ductinghaving inlet and outlet means for affording passage of the gas flow in acommon general direction, a combustion chamber within said ducting anddefining therein a zone of at least initial combustion, a gas flowpassage defined within said ducting but without said chamber bystructure distinct from both and extending in the general direction ofgas flow in overlapping relationship with said combustion zone, saidpassage having inlet means at its upstream end for admitting at least apart of the combustion-supporting gas flow, and outlet means at itsdownstream end for delivering such gas flow into a continuation of thedirection, a plurality of combustion chambers" within said ducting andeach defining therein a zone of at least initial combustion, saidchambers being arranged in annular series about an axis corresponding tothe general direction of gas flow, and a plurality of diifusion nozzleswithin said ducting but without said chambers and struca'f tweenadjacent combustion chambers and extending in the general direction ofgas flow therebetween, each being connected to said gas inlet means anddischarging gas into said ducting at a point therein downstream of theupstream ends of said combustion chambers, and each affording a flowpassage of increasingcross section area progressively in a downstreamdirection to effect controlled diffusion of the gas flow passingtherethrough.

3. A combustion apparatus as claimed in claim 2, wherein a compressorsupplies the gas flow, said compressor having a plurality of outletports arranged in annular series coaxial with said combustion chambers,said ports being each connected to one of said nozzles and discharginggas into said ducting therethrough.

4. A combustion apparatus as claimed in claim 2, wherein a compressorsupplies the gas flow, said compressor having a plurality of outletports arranged in annular series coaxial with said combustion chambers,said ports being each connected to one of said nozzles anddischarginggas into said ducting therethrough, each nestle receiving'f'ch'anging in the downstream direction from a section corresponding tothat of the combustion turally distinct therefrom, said nozzles eachbeing, a

gas from a number (at least two) of ports which number is the same foreach nozzle.

5. A combustion apparatus as claimed in claim 2, wherein said gasducting defines a single annulus enclosing all said combustion chambersand nozzles, and extendingin the general direction of gas flow.

6 A combustion apparatus as claimed in claim 2, wherein a rotarycompressor supplies the gas flow, and a turbine coaxial with saidcompressor receives the combustion gases, said gas ducting andcombustion chambers being arranged as an annular structure coaxial withand between the turbine and compressor.

7. A combustion apparatus as claimed in claim 2, wherein the gas ductingdefines an annulus enclosing said combustion chambers, and furthercomprising a diaphragm extending across said annulus, aperturesafl'orded in said diaphragm through which the combustion gases pass, andcombustion chamber supporting and locating means associated with thediaphragm in the region of each aperture whereby a chamber is ail'ordedfreedom to slide relatively thereto in the general direction of gas flowwhile being located in directions normal thereto in alignment with saidaperture.

8. A combustion apparatus as claimed in claim 2, wherein the gas ductingdefines an annulus enclosing said combustion chambers, and furthercomprising a diaphragm extending across said annulus, apertures affordedin said diaphragm through which the combustion gases pass, combustionchamber supporting and locating means associated with the diaphragm inthe region of each aperture whereby a chamber is afforded freedom toslide relatively thereto in the general direction of gas flow whilebeing located in directions normal thereto in alignment with saidaperture, and an outlet chute associated with each combustion chamberdownstream of said diaphragm to receive the combustion gases from thechamber, means supporting and locating said chute in alignment with saidcombustion chamber, said outlet chute chambertofthatof a segment of anannulus, the

.-outlets from" said chutes collectively forming a complete annulus."

9. A combustion a aratus as claimed in claim accommodated at leastpartly within a space be pp 2, v wherein the gas ducting defines anannulus enclosing said combustion chambers, and further comprising adiaphragm extending across said annulus, apertures aiforded in saiddiaphragm through which the combustion gases pass, combustion chambersupporting and locating means associated with the diaphragm in theregion of each aperture whereby a chamber is afforded freedom to sliderelatively thereto in the general direction of gas flow while beinglocated in directions normal thereto in alignment with said aperture, anoutlet chute associated with each' combustion chamber downstream of saiddiaphragm to receive the combustion gases from,the chamber, and meanssupporting and locating said chute in alignment with said combustionchamber, said outlet chute changing in the downstream direction from asection corresponding to that of the combustion chamber to that of asegment of an annulus, the outlets from said chutes collectively forminga complete annulus, said means supporting and locating said combustionchamber or outlet chute comprising a seating abounding the associatedour:

7 aperture aflording a spigot and socket engage- REFERENCES CITED mentwith Said combustmn chamber chute- The following references are ofrecord in the 10. A combustion apparatus as claimed in I claim 1,wherein means are provided for injecting me 0 this patent fuel fromwithin the combustion zone and in an 5 UNITED STATES PATENTS upstreamdirection into the upstream limiting Number Name Dat region Of saidzone. 2,404,334 Whittle July 16, 1948 D NOR w 2,435,836 Johnson Feb. 10,1948 PETER FREDERICK ASHWOOD. 1o FOREIGN PATENTS HENRY COWAN. NumberCountry Date 585,763 Great Britain Feb. 24, 1947

